A disk drive or direct access storage device ("DASD") includes one or more thin film magnetic disks stacked on a spindle. A plurality of thin film layers are deposited onto a rigid substrate typically including an underlayer, a magnetic layer and a protective overcoat. Data is stored on these disks by magnetizing portions of the disk in a pattern which reflects the data.
The read and write heads are contained in a small ceramic element called a slider. When operating at full speed the slider typically is flown at a height of approximately one to two millionths of an inch from the surface of the disk as data is written or read from the disk. During startup and shutdown processes when the disk is either not rotating or is rotating too slowly to provide the air bearing, the slider may be in contact with the disk. Shock events can also cause the slider to contact the disk. There are also proposals to operate drives with the slider essentially in contact with the disk surface.
The slider and the disk, therefore, require a wear-resistant coating. Various materials have been explored for use as disk overcoats including carbon, silicon dioxide and various other oxides. Hydrogenation of the sputtered carbon film is known to improve the durability of the thin-films, as discussed in U.S. Pat. No. 5,045,165 to Yamashita. Yamashita found that the addition of 20% hydrogen into the sputtering chamber resulted in significant hydrogen being incorporated into the film with the carbon. Kokai, et al., in U.S. Pat. No. 4,755,426 teach use a carbonaceous overcoat consisting essentially of carbon, hydrogen and oxygen.
Ishikawa, et al., (IEEE Trans. Mag-22, No. 5, September 1986) disclose the use a two layer overcoat with the first layer being either sputtered carbon or PCVD carbon followed by a second PCVD carbon layer deposited using higher pressure acetylene. The PCVD carbon was obtained by DC or RF discharge chamber in an acetylene atmosphere. The upper layer was deposited using a high pressure of acetylene to result in a soft film. When PCVD carbon was used as the first layer it was deposited using a lower pressure of acetylene. Similarly, Nakamura, et al., (co-authors of the IEEE article) in U.S. Pat. No. 4,804,590 teach the use of two layers of carbonaceous material obtained by DC or RF discharge chamber in an acetylene atmosphere with the lower layer being comparatively hard and the upper layer being softer. The softer more lubricative layer is a PCVD carbonaceous film contain 6 at. % or more of either or both hydrogen and fluorine while the harder layer contains 5 at. % or less of hydrogen and fluorine. To provide better adhesion the use of an intermediate layer of chromium or titanium over the magnetic layer was suggested.
Itoh in U.S. Pat. No. 5,368,937 in connection with integrated circuits and thermal heads describes the use of increasing bias voltage during the plasma CVD process to generate an amorphous hydrogenated carbon layer in which the hardness increases toward the surface of the film. One of method of increasing the bias voltage is said to be to decrease the pressure of the reactive gas in the chamber.
Seki, et al., describe a carbon film which has a decreasing dopant concentration in the direction away from the surface.
The presence of hydrogen reduces the adhesion of the thin-film to the underlying magnetic layer. Moreover, hardness and density are reduced by the presence of hydrogen in certain percentage ranges.